1. Field
The present inventions relate generally to reinforcing fabrics for power transmission belts and, more specifically, to a double knit twill fabric for reinforcing power transmission belts and the belts that are constructed using this fabric.
2. Related Art
Cogged or grooved power transmission belts, such as continuously variable transmission (CVT) belts, timing belts and poly v-belts, often utilize a cog and groove covering fabric along the inner portion of the belt which contacts the drive motor shaft to prevent cracking and to provide reinforcement and wear resistance during belt use. The fabric substrate is typically composed of polyamide yarns and can achieve high degrees of elongation in a single direction, even at relatively low stresses.
The fabric substrate's ability to stretch allows for the formation of each cog/groove during the compression or expansion molding that takes place during the belt cure cycle as the belt is being formed. In addition, the fabric substrate's elasticity provides resilience and flexural integrity during belt use.
Current woven fabric substrates have limitations. For one, elongation is generally limited to only one direction for such fabrics, which restricts cog/groove formation during production. In addition, while woven fabric has excellent performance strike-through characteristics, it is quite expensive to manufacture. Knitted fabrics could be much cheaper to manufacture and provide some elongation in both the machine and the cross-machine direction. However, because knitted fabrics have a propensity to stretch, inter-yarn interstitial spaces are created, which permits excessive strike-through. This is also an unacceptable characteristic.
Thus, there remains a need for a new and improved fabric substrate for use with power transmission belts that provides elongation in both the machine and cross-machine direction while, at the same time limits strike-through.